“The biggest problem is you have people that do not have a trained dog. They’re taking untrained dogs out there and they’re causing problems,” Brodie said. “They’re saying they’re service dogs, but they’re not.”

The dogs’ trainer took the three to a veterinarian office, where she left the dogs in the car while she walked in to visit with coworkers. She left the car on with the air conditioning running and had a sensor that was supposed to go off if the car got too hot, the dog owners said.

However, the sensor was not working. The car died and the dogs were left in the nearly 100 degree heat, where they died. Fort Worth police are investigating the dogs’ deaths.

“This thing has gotten out of hand,” said Jeff Younggren, a psychologist and clinical professor at the University of New Mexico, who has conducted several studies on the subject of emotional support animals.

The number of passengers flying with emotional support animals on the nation’s airlines has surged. United Airlines, one of the biggest carriers, saw a 75% increase last year compared with 2016. The trend has been accompanied by more incidents of animals urinating, defecating, biting, barking and lunging on planes. A passenger was even mauled by a 50-pound dog on a Delta flight last year.

Coren, in his book, “The Intelligence of Dogs,” featured the results of a lengthy survey of 199 dog obedience judges. The responses, he said, were remarkably consistent; however, he noted that many judges pointed out that there are exceptions in every breed and that a lot comes down to training.